QCX assembly Rev 1.08
104
5. Circuit design of the QCX
5.1
Block diagram and summary
This CW transceiver is a high performance, yet simple and low cost, analogue design. The
transmitter uses a high efficiency Class-E amplifier which results in low current draw on transmit,
and inexpensive transistors with no heatsinks.
The receiver is a direct conversion type utilising the famous high performance Quadrature
Sampling Detector, also known sometimes as the “Tayloe Detector” or even “I-Q Mixer”. This
receiver front end architecture has been used in the early Flex Software Defined Radios, Softrock
series, Norcal NC2030 and many oth
er SDR’s and other high performance front ends. The
detector has very high third order intercept (IP3) and dynamic range, as well as low loss.
The resulting I & Q outputs are at audio baseband and go through a 90-degree phase shift
network which cancels the unwanted sideband. A 200Hz bandwidth CW filter is followed by more
amplification and drives common earphones.
The oscillators in the transceiver are provided by the modern Si5351A digital phase locked loop IC
controlled by the microcontroller.
Permeating the entire design is microprocessor control by the ATmega328P microcontroller. This
allows implementation of a large number of functions normally only found in radios costing 10-
100x the price!
A really nice feature of the design is the built-in alignment and test equipment, which make it
possible to build, align and even debug the assembly of the radio, all with NO additional test
equipment.
Summary of Contents for QCX 5W CW
Page 9: ...QCX assembly Rev 1 08 9...
Page 10: ...QCX assembly Rev 1 08 10...
Page 12: ...QCX assembly Rev 1 08 12...
Page 50: ...QCX assembly Rev 1 08 50...
Page 105: ...QCX assembly Rev 1 08 105...
